Re: Uniquness of ctid

On Wed, Jul 19, 2023 at 2:31 PM PG Doc comments form <noreply(at)postgresql(dot)org>
wrote:

> The following documentation comment has been logged on the website:
>
> Page: https://www.postgresql.org/docs/15/ddl-system-columns.html
> Description:
>
> Hi,
> Looking at the explanation abour ctid, it is "The physical location of the
> row version within its table. "
> From that line, I think ctid is unique in the table.
>

Unique but not stable - if you give your actual record an ID value the
associated ctid for it may very well change over time and a given ctid can
be associated with any number of IDs

> And I also think ctid might be unique across the database since it is the
> physical location.
>

The concept doesn't even apply - the value itself only makes sense within a
given physical table. i.e., the table is implied. It's like saying "I live
at 123 Main St." to someone. Sure in any given place there can only be a
single 123 Main St. but that really isn't useful by itself. And to extend
back to the previous point, you may live there now but you will likely have
a different address in the future and someone else will have 123 Main St.

David J.